The need for chemical treatment of solid materials with gaseous reagents under conditions of elevated pressure and/or temperature arises in many processing applications. Examples include high pressure and temperature steam treatments of wood and wood pulp in pulp and paper manufacture and other utilizations of wood, the steam treatment of particulate materials of minerals such as gravel, stones and sand for cleaning and purifying processes, the treatment of mineral ores with gaseous reagents such as steam or acids to enrich the metal content thereof and aid in the extraction of metals therefrom, treatment of animal products with steam for rendering purposes, treatment of bitumens, coals, tar sands and other fuel values with gaseous reagents such as hydrocarbons for enrichment purposes, plasticizing treatments and the like. Where such processes are to be conducted continuously, and the product at the gaseous treatment is in a finely divided form, problems arise with the discharge of the finely divided product after treatment. Losses of gaseous reagent and gas pressures and temperatures from the pressurized reactor vessel as the treated product is continuously discharged therefrom need to be minimized, for economic reasons among others.
A typical example of such a process is the treatment of wood chips with steam at elevated pressures and temperatures, in a continuously operating pressurized steam digestor vessel, e.g. to prepare cellulose fibrous product. The resulting product is in finely divided fibrous form, and has a variety of different potential uses (insulation, animal fodder, etc.). The economics of the process require that the vessel be maintained at elevated temperatures and steam pressures, and that the fibrous product after treatment be continuously withdrawn from the vessel without excessive losses of steam pressures therefrom. The steam pressures in the vessel may be in the 200-300 psig range. The finely divided product materials must be discharged in such a manner that the physical nature of the product is not damaged, and that excessive wear and tear on apparatus parts is avoided.